High strength fibers from chitin derivatives

ABSTRACT

High tenacity chitin acetate/formate and chitosan acetate/formate fibers and the process for making such fibers are disclosed.

RELATED APPLICATIONS

This application is a division of my application Ser. No. 07/090,144,filed Aug. 27, 1987, now abandoned, which is a division of myapplication Ser. No. 942,442, filed Dec. 16, 1986, now abandoned.

DESCRIPTION

1. Technical Field

This invention relates to high strength fibers from chitin derivativesand the process for making those fibers.

2. Background

Chitin (poly-N-acetyl-D-glucosamine) is a polysaccharide widelydistributed in nature and is a major component of the cell wall ofvarious fungi as well as the shell of insects and crustaceans. Chitinhas been extracted and purified from its various sources and has beenformed into potentially useful articles such as fibers for medicalsutures. Chitin-based fibers having both high tensile strength and highmodulus of elasticity prepared directly without post fiber treatmentwould be highly desirable.

Previous work to provide high strength chitin fibers has included theafter-treatment of wet-spun chitin fibers in a second coagulation bathas described in U.S. Pat. No. 4,431,601 or by drawing the fiber asdescribed in Japanese Patent Pub. (Kokai) No. 58-214,513.

Method to produce chitosan (poly-D-glucosamine) and chitin acetate(poly-N-acetyl-O-acetyl-D-glycosamine) are known and methods forspinning chitosan and chitin acetate into fibers are described inJapanese Patent Pubs. (Kokai) No. 56-106901 and No. 53-126063,respectively.

In the polysaccharide art, optically anisotropic spinning solutions fromcellulose and cellulose acetate have been disclosed. An object in thecellulose art was to provide a concentrated solution of highlypolymerized cellulose triacetate as well as a large degree of acetatesubstitutions in order to produce high strength fibers are described inU.S. Pat. No. 4,464,323.

It has now been discovered that by forming a fiber from the mixedderivative of chitin or chitosan acetate/formate that significantlyhigher tenacity can be obtained. Higher tenacity chitin acetate fibersare obtainable by lowering the degree of substitution. This iscompletely unexpected in light of U.S. Pat. No. 4,464,323.

SUMMARY OF THE INVENTION

Chitin acetate/formate and chitosan acetate/formate polymers have nowbeen discovered. Chitin acetate/formate and chitosan acetate/formatepolymers can be spun into fibers having tenacities at least 4 g/den andmoduli at least 100 g/den. The tenacities can be reached directly forthe as-spun fiber and are preferably at least 5.5 g/den for the chitinacetate/formate fiber and at least 6 g/den for the chitosanacetate/formate fiber. The moduli for chitin acetate/formate and forchitosan acetate/formate is preferably 150 g/den. The process for makingchitosan acetate/formate polymer suitable for preparing fibers havingas-spun tenacities greater than 4 g/den comprises the steps of addingformic acid, acetic anhydride and acetic acid to chitosan.

Chitin acetate fiber having a tenacity of at least 4 g/den, and amodulus of at least 100 g/den and a degree of acetylation of less than2.2 has also been discovered.

Purified chitin is derivatized to provide chitin acetate, chitinacetate/formate, and chitosan acetate/formate. These chitin derivativescan be extruded from optically anisotropic solutions through an air gapand into a coagulating bath to form high strength fibers. Fibers madefrom the acetate/formate derivatives or low degree of substitutionchitin acetate show increased strength when compared to non-derivatizedchitin fibers or high degree of substitution chitin acetate.

Chitin, when isolated in high molecular weight form, is soluble at lowconcentration in only a limited number of specialized solvent systems.In order to enhance the solubility of chitin-based polymers, it isdesirable to place organic substituents on the free amine or hydroxygroups of chitin or chitosan. These substituents perform two functions.First, they provide organic pendant groups to facilitate dissolution inorganic solvent systems, e.g. trichloroacetic acid/methylene chloride.Second, the presence of such substituents disrupts the crystalline,strongly hydrogen-bonded structure of native chitin, which itselfconstitutes a significant barrier to dissolution. Mixed substituentderivatives such as acetate/formate are especially attractive in aidingthe dissolution and spinning processes in that their fiber-formingability and viscosity are very well suited for spinning atconcentrations exceeding 10 wt. % and would therefore be attractive forcommercial scale manufacture. In addition, it is observed that the lossof molecular weight as evidenced by a decrease in solution viscositywith time is greatly reduced with the mixed substituent derivatives.

Chitin refers to poly-N-acetyl-D-glycosamine wherein the degree ofN-acetyl substitution is from 0.75-1.0. Though chitin is found naturallywith the C5-C6 bond in the D-configuration, the chemistry defined hereinwould be just as applicable to an L-form and is not intended to belimited to the D-form.

Chitin derivatives are referred to herein in the following manner:chitin acetate refers to poly-N-acetyl-O-acetyl-D-glycosamine whereinthe O-acetyl group can be substituted at the C3 and C6 position of themonomer to a varying degree, with a degree of O-acetylation ranging fromabout 0.05 to 2.0; chitin acetate/formate refers topoly-N-acetyl-O-acetyl-N-formyl-O-formyl-D-glycosamine wherein theO-acetyl and O-formyl substitution occurs at the C3 and C6 ring-positionof the monomer in a random distribution within the polymer to a varyingdegree, with a degree of acetylation ranging from about 0.05 to 2.0 anda degree of formylation ranging from about 0 to 1.95 and wherein theN-acetyl substitution is a degree of acetylation ranging from about 0.75to 1.0 wherein the N-formyl substitution is a degree of formylationranging from about 0 to 0.25 and wherein the total degree of formylationis greater than 0.05. Chitosan is obtained by de-N-acetylation of chitinand refers to poly-D-glucosamine; and chitosan acetate/formate refers topoly-N-formyl-N-acetyl-O-acetyl-O formyl-D-glycosamine wherein theO-acetyl and O-formyl substitution occurs at the C3 and C6 position ofthe monomer in a random distribution within the polymer to a varyingdegree, with a degree of acetylation ranging from about 0 to 2.0,preferably 0.05 to 2.0, and a degree of formylation ranging from about 0to 2.0 and wherein the N-acetyl substitution is a degree of acetylationranging from about 0 to 0.75, the N-formyl substitution is a degree offormylation ranging from about 0 to 1.0 and wherein the total degree ofacetylation is greater than 0.05 and the total degree of formulation isgreater than 0.05. The total degree of formyl and acetyl groupsubstitution onto the above-described chitin derivatives is determinedby the types and concentration of reactants and catalysts used for thepreparation of each polymer.

In the preparation of fibers, optically anisotropic solutions of eachchitin derivative were prepared and then extruded through a spinneretinto a coagulation bath to form fibers which were then wound ontobobbins.

The anisotropic spinning solutions were prepared by dissolving thechitin derivative into a solvent comprising trichloroaceticacid/methylene chloride. The solutions were judged to be anisotropic if,when sandwiched between a microscope slide and cover slip, they werebirefringent when viewed between crossed polarizers. Generally, chitinderivatives were found to form optically anisotropic solutions whendissolved at weight percents greater than 10% in a 60/40 (w/w)trichloroacetic acid/methylene chloride solvent.

It is recognized that both the molecular weight and pattern ofsubstitution of chitin polymers or chitin derivative polymers willprobably determine their solubility in any particular solvent and alsothe concentrations at which optical anisotropy is observed. Also, eventhough a 60/40 (w/w) trichloroacetic acid/methylene chloride solvent isused for most of the work described herein, other solvents for chitin orits derivatives could be used.

The chitin derivative chitosan acetate/formate can be formed by reactingchitosan in the presence of acetic acid, formic acid and aceticanhydride. The order of addition and relative quantities of thesereactants is important in determining the product obtained.

When chitosan is dissolved first in an aqueous mixture of acetic andformic acids followed by the addition of acetic anhydride, predominantlyN-formylation and O-formylation occur, accompanied by some O-acetylsubstitution. Rather, if the chitosan is first dissolved in an aqueoussolution of acetic acid and acetic anhydride followed by the addition offormic acid, a mixture of N-acetylation, O-acetylation, N-formylationand O-formylation is obtained.

The ratio of acetic acid to formic acid in the above solutions willdetermine the relative degree of substitution obtained. In addition, thepredominant N-substituted species is determined by which correspondingacid (acetic or formic) is added first to the chitosan in the presenceof acetic anhydride; the level of acetic anhydride being rate limiting.

The chitin derivative, chitin acetate/formate, is formed by reactingformic acid and acetic anhydride with chitin in the presence of an acidcatalyst. Acetylation of chitin by acetic anhydride in the presence ofan acid catalyst occurs rapidly. Therefore, to control the level offormylation occurring on the chitin, the formic acid can be added firstto the chitin in the presence of an acid catalyst and allowingsufficient time for formylation to occur before the subsequent additionof acetic anhydride. An acid catalyst useful in these reactions isperchloric acid.

The coagulation bath used during fiber formation consisted of coldmethanol, which is a non-solvent for chitin and its derivatives. Thecoagulation bath was between 20 and 30 inches in length. Any suitablenon-solvent for chitin or its derivatives could be used in place ofmethanol for the purpose of coagulating the fiber spinning solution.

There are many parameters which can be varied in the spinning scheme andone could readily adjust spinneret orifice diameters, length of the airgap spacing, jet velocity, bath conditions, ratio of windup speeds tojet velocity, as well as other parameters in order to optimize variousphysical properties of the fibers of this invention.

The chitin derivative polymers produced according to the presentinvention are spun from anisotropic solution and form high strengthfibers. Fibers prepared from chitosan acetate/formate have tensileproperties which typically fall between 4-8 g/d tenacity and 150-250 g/dinitial modulus. It is expected that articles other than fibers, such ascast or molded products, could be produced from the polymers describedherein and may also demonstrate high strength properties.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an apparatus for air-gap spinning ofanisotropic solutions of chitin and chitin derivatives.

FIG. 2 is a schematic diagram of a twin cell apparatus for air-gapspinning of anisotropic solutions of chitin and chitosan derivatives.

FIG. 3 is a schematic diagram of a mixing plate used in conjunction withthe apparatus of FIG. 2.

DETAILED DESCRIPTION OF THE DRAWING

In using the apparatus of FIG. 1 an anisotropic solution of chitin or achitin derivative was placed in spin cell (G). A piston (D) activated byhydraulic press (F) and associated with piston travel indicator (E) waspositioned over the surface of the solution, excess air expelled fromthe top of the cell and the cell sealed. The spin cell was fitted at thebottom with the following screens (A) for solution filtration: four tosix 325-mesh screens. The filtered solution was then passed into aspinneret pack (B) containing two or three 325-mesh screens. Solutionswere extruded through an air gap at a controlled rate into a static bath(C) using a metering pump to supply pressure at piston (D). The fiberwas passed around a pin (H), pulled through the bath, passed under asecond pin (I) and wound onto a bobbin. The air gap between thespinneret face and the coagulation bath was typically 0.6 to 2.0 cm. Thecoagulation bath temperature was generally held below 100° C. withspecific values as given in the examples.

In using the apparatus of FIG. 2, filter plate (J) is replaced by mixingplate (R). Polymer dope is placed in cylinder bore (T) and then piston(D) and cap plate (L) is fitted to the spin cell (G). A driver fluid(e.g. water) is pumped into the upper part of bore (T) through feed line(F). The piston (D) is displaced by the driver fluid, thereby pushingthe polymer dope through passages (W), (S) in mixing plate (R) and thenthrough passage (K) in distribution plate (M) into second cylinder bore(U). This process is then reversed by pumping fluid through feed line(X). The aforementioned forward and reverse process is repeated severaltimes to effect a mixing of the polymer dope. Component (E) acts tosense the position of cylinder (D).

After mixing is complete (about 30 cycles), mixing plate (R) is replacedby filter plate (J) and polymer dope is extruded from bore (T) throughpassage (W), through filter pack (A) containing 2 Dutch Twill Weave165×800 mesh screens, through passage (Y) in filter plate (J) andpassage (Z) in spinneret mounting plate (O) and out of spin cell (G)through spinneret (B). The extruded dope is spun into a bath and takenup as described for FIG. 1. Pressure of the polymer dope during spinningis measured by pressure transducer (P).

TEST METHODS

Inherent viscosity (I.V.) is calculated using the formula:

Inherent viscosity η_(inh) =(Ln η_(r)·l)/C where C is the polymerconcentration in grams of polymer per deciliter of solvent. The relativeviscosity (η_(r)·l) is determined by measuring the flow time in secondsusing a standard viscometer of a solution of 0.5 (except whereindicated) of the polymer in 100 ml hexafluoroisopropanol at 30° C. anddividing by the flow time in seconds for the pure solvent. The units ofinherent viscosity are dl/g.

Jet Velocity (J.V.) is the average exit velocity of the spinningsolution from the spinneret capillary as calculated from the volume ofsolution passing through an orifice per unit time and from thecross-sectional area of the orifice and is reported as meters perminute.

Filament tensile properties were measured using a recordingstress-strain analyzer at 70° F. (21.1° C.) and 65% relative humidity.Gauge length was 1.0 in (2.54 cm), and rate of elongation was 10%/min.Results are reported as T/E/M. Tenacity T is break tenacity in g/den,Elongation (E) is elongation-at-break expressed as the percentage bywhich initial length increased, and Modulus (M) is initial tensilemodulus in g/den. Average tensile properties for at least three filamentsamples are reported. The test is further described in ASTM D2102-79part 33, 1981.

Degree of Substitution (DS) of acetate or formate is determined byproton-NMR in the following manner:

The spectra are determined in deuterated trifluoracetic acid solvent andusing tetramethylsilane (TMS) as a standard. The D.S. is determined byintegrating the area due to the protons on carbons C₁ through C₆ of theglucosamine derivative (6.0 to 3.0 ppm) and comparing it with the totalarea due to the methyl group protons (2.5 to 2.0 ppm) using thefollowing formula:

    D.S.=(M/(G/7))/3

where:

M=area of methyl group protons

G=area of the protons on carbons C₁

through C₆ of the glucosamine derivative

The formyl protons are observed at about 8.4 ppm for the amide and atabout 8.2 ppm for the ester. The D.S. of formyl groups is determined ina similar fashion using the following formula:

    D.S.=F/(G/7)

where:

F=area of formyl protons

G=area of the protons on carbons C₁

through C₆ of the glucosamine derivative

To determine the relative amounts of acetyl and formyl content in themixed derivatives both formulas are used.

EXAMPLES RUN A

Chitin was isolated from shrimp shells and spun into fiber according tothe following procedures:

Isolation of Chitin

Shrimp shells obtained from Gulf Cities Fisheries of Pascagoula, Miss.were placed in large containers and soaked in acetone for 5 to 7 days,after which the acetone was filtered off and the shells rinsed withadditional acetone to remove as much pigment as possible. The shellswere then air dried for 72 hours. The dried shells were ground into aflake using a Abbe cutter. The ground shells (500 g) were decalcified bytreatment with ice cold 10% hydrochloric acid (4 to 6 l) with stirringfor 20 minutes. The liquid was then removed by filtering and the shellsrinsed with water. This acid treatment was repeated and the decalcifiedshells were rinsed with water until neutral and allowed to air dry. Thedry solid was suspended in 2.5 l of 3% sodium hydroxide in a 5 l flaskand heated at 100° C. for 2 hours. The suspension was then filtered andthe remaining solid washed with water. This caustic treatment wasrepeated and the chitin obtained was washed with water until neutral.The chitin was then washed successively with methanol and acetone, airdried and lastly dried in a vacuum oven for about 12 hours at 120° C.

Spinning

Chitin obtained by the above procedure was dissolved at 24° C. in a60/40 (w/w) trichloroacetic acid/methylene chloride mixture, to form asolution containing 13.5% solids. The solution was tested and found tobe anisotropic.

The chitin solution above was extruded into fibers using the apparatusrepresented by FIG. 1 and described previously. The solution wasextruded through 0.004" diameter holes of a 10-hole spinneret at a jetvelocity of 15.2M/min., passed through a 1.25 cm air gap, into a 0° C.methanol bath and wound onto bobbins at a rate of 15.5M/min.

Fiber properties was measured as described above and are reported inTable I.

RUN B

Chitin acetate with a high degree of substitution of acetyl groups wassynthesized and spun into fiber by the following method:

Preparation of Chitin Acetate

200 ml of reagent grade methylene chloride, 400 ml of reagent gradeacetic anhydride, and 125 ml of glacial acetic acid were added to a 1 lresin kettle equipped with a stirrer and nitrogen inlet. The mixture wascooled to about 0° C. in a methanol bath and 20 g of chitin, prepared asin Run A, were added. 6 ml of 70% perchloric acid were then added slowlyand the mixture was stirred about 12 hours. After stirring, the mixturewas filtered on a fritted Buchner funnel and excess acetic anhydride wasremoved by aspiration. The solid was washed thoroughly with methanol,acetone, 10% sodium bicarbonate, water, and lastly acetone, after whichthe solvent was removed by aspiration. The remaining solid was then airdried for about 12 hours to give 25 g of chitin acetate as a whitesolid. The inherent viscosity of the polymer was 5.72 dl/g and thedegree of substitution was 2.95.

Spinning

Chitin acetate prepared by the above procedure was spun as in Run Ausing the apparatus represented by FIG. 2 with the different spinningparameters listed in Table 2.

Fiber properties were measured as described above and reported in TableI.

EXAMPLE 1

Chitin acetate with a relatively low degree of substitution of acetylgroups on chitin was synthesized and spun into fiber by the followingmethod:

Preparation of Chitin Acetate

200 ml of reagent grade methylene chloride, 400 ml of reagent gradeacetic anhydride, and 125 ml of glacial acetic acid were added to a 1 lresin kettle equipped with a stirrer and nitrogen inlet. The mixture wascooled to about 0° C. in a methanol bath and 20 g of chitin, prepared asin Example 1, were added. 3 ml of 70% perchloric acid were then addedslowly and the mixture was stirred about 12 hours. After stirring, themixture was filtered on a fritted Buchner funnel and excess aceticanhydride was removed by aspiration. The solid was washed thoroughlywith methanol, acetone, 10% sodium bicarbonate, water, and lastlyacetone, after which all of the solvent was removed by aspiration forabout 12 hours to give 25 g of chitin acetate as a white solid. Theinherent viscosity of the polymer was 8.76 and the degree ofsubstitution was 2.0.

Spinning

Chitin acetate prepared by the above procedure was spun as in Run Ausing the apparatus represented by FIG. 2 with the different spinningparameters listed in Table 2.

Fiber properties were measured as described above and reported in TableI.

EXAMPLE 2. Isolation of Chitin

Wet shrimp shell waste (25 kg) was sorted manually to remove extraneoussubstances and boiled in water for 2 hours. The shells were collected byvacuum filtration and placed into cheesecloth pouches. Using one-half ofthe batch at a time, the shells were then boiled in 2% NaOH (50 l) undera nitrogen atmosphere for 1 hour, collected, pressed out and washed oncewith water. The shells were then boiled for 9 hours in 2% NaOH (50 l)under nitrogen for a second time, collected, pressed out, washed inwater and immersed in 50 l 10% acetic acid for 1 hour at roomtemperature. The shells were collected by filtration, washed twice morein water and pressed out. They were finally suspended in acetone (4 l),collected by filtration, washed once more with clean acetone and allowedto air dry. The yield was 1.2 kg dry chitin.

Preparation of Chitin Acetate

Chitin (50 g) prepared as described above was ground in two steps topass through a 0.5 mm screen. The ground chitin was placed in a Soxhletextractor and extracted with acetone until the extract was clear. Afterair drying, the chitin powder was washed twice with methanol, pressedout and heated to 77° C. in 15% methanolic potassium hydroxide for 1hour under nitrogen. The powder was collected by filtration, pressedout, washed once with water followed by two washes in glacial aceticacid. After the final wash, the powder was pressed out and suspendedusing methods described above in cooled acetic anhydride (500 ml) andmethylene chloride (500 ml) containing perchloric acid (2 ml) all at-22° C. After 16 hours, the temperature was raised to 13° C. and thereactants allowed to stir for an additional 24 hours reaching a finaltemperature of 18° C. The polymer was collected by filtration, pressedout and washed twice with methyl alcohol. The product was then washedonce in 5% sodium bicarbonate, followed by two washes in water and afinal wash in acetone. The product was dried in a vacuum at 55° C. Theyield was 57 g. D.S.=1.4 based on NMR analysis.

Spinning

Chitin acetate prepared as described above was spun using the method ofRun A and the equipment described by FIG. 1. The spinning solvent was60/40 w/w trichloroacetic acid/methylene chloride. Pertinent spinningparameters appear in Table II.

Fiber properties were measured as described above and appear in Table I.

EXAMPLE 3

Chitin acetate/formate was prepared from chitin and then spun into fiberby the following method:

Preparation of Chitin Acetate/Formate

200 ml of reagent grade methylene chloride and 255 ml of formic acid(95-98% were added to a 1 l resin kettle equipped with a stirrer andnitrogen inlet and cooled in a refrigerated bath to 0° C. 280 ml ofacetic anhydride were added to the bath, allowed to cool to 0° C., andthen 20 g of chitin prepared as in Run A were added followed by the slowaddition of 6 ml of 70% perchloric acid. The mixture was stirred forabout 12 hours at 0° C. The suspension was washed thoroughly withmethanol, acetone, 10% sodium bicarbonate, water, and lastly acetone.After removing the solvent by aspiration, the solid was aid dried forabout 12 hours and yielded 24 g of chitin acetate/formate as a whitesolid.

The inherent viscosity of the polymer was 11.4 dl/g and the degree ofsubstitution was 2.5/0.5 (acetyl/formyl).

Spinning

Chitin acetate/formate prepared by the above procedure was spun the sameas in Run A using the apparatus represented by FIG. 2 with the differentspinning parameters listed in Table II.

Fiber properties were measured as described above and reported in TableI.

EXAMPLE 4

Chitosan acetate/formate was prepared from chitosan which itself wasprepared from chitin and then the chitosan acetate/formate was spun intofibers, per the following procedures:

Preparation of Chitosan

Shrimp shells were washed in acetone and ground into a flake asdescribed in Run A. The washed and cut shells (310 g) were then treatedwith ice cold 9% hydrochloric acid (2 l water, 1 l ice chips, 1 l 37%HCl) in a large container for 20 minutes. The solution was filtered andthe remaining solid rinsed with water. This acid treatment was repeated,after which the solid was washed with water until neutral and thenwashed with acetone and finally air dried. The resulting solid wastreated with 2 l of 50% sodium hydroxide at 100° C. for 2 hours. Thesuspension was filtered and the remaining solid was rinsed with water.This caustic treatment was repeated a second time and the solid wascollected by filtration, washed until neutral with water, and thenwashed with methanol and acetone and allowed to air dry. This procedureyielded 86 g of chitosan as a white solid.

The inherent viscosity of the chitosan was 11.3 dl/g in 50% aqueousacetic acid.

Preparation of Chitosan Acetate/Formate

750 ml of 95-98% formic acid and 40 g of chitosan prepared above wereadded in a 4 l resin kettle. The mixture was stirred under nitrogen in arefrigerated bath at 0° C. for 1.5 hours until all the polymer wasdissolved.

250 ml of glacial acetic acid were then added and the mixture stirreduntil a homogeneous solution was obtained. The mixture was stirred anadditional 30 min., 500 ml of reagent grade acetic anhydride were addedand then the mixture was stirred for about 12 hours at 0° C. Theresulting gel was broken up and soaked in methanol (6 liters) for a fewhours to precipitate the polymer. The polymer was filtered and the solidgel chopped in a blender. The precipitated polymer was washed thoroughlywith methanol several times, and then with acetone. The solid wasaspirated to remove excess solvent and then allowed to air dryovernight. The yield was 53 g of chitosan acetate/ formate as a whitesolid.

The inherent viscosity of the polymer was 10.8 dl/g and the degree ofsubstitution was 0.4/2.3 (acetyl/formyl).

Spinning

Chitosan acetate/formate prepared by the above procedure was spun as inRun A using the apparatus represented by FIG. 2 with the differentspinning parameters listed in Table II.

Fiber properties were measured as described above and reported in TableI.

EXAMPLE 5

Chitosan acetate/formate was prepared according to the general procedurein Example 4 with the changes noted below.

750 g of 95-98% formic acid and 40 g of chitosan were mixed in a 4 lresin kettle at 0° C. Once the chitosan was well dispersed 500 ml ofacetic anhydride were added and the reaction allowed to stir for 95hours at 0° C. At that time the polymer was essentially completely insolution and was isolated by precipitation into cold methyl alcohol (6liters at 0° C.). The white product was collected by vacuum filtration,then washed twice with water, followed by another wash in methyl alcoholand a final wash in acetone. The product was allowed to air dry yieldinga white fibrous solid.

Spinning

Chitosan acetate/formate prepared by the above procedure was spun usingthe method of Example 1 and the equipment described by FIG. 1. Thespinning solvent was 49:51 w/w trichloroacetic acid/methylene chloride.Other pertinent spinning parameters appear in Table II.

Fiber properties were measured as described above and appear in Table I.

                  TABLE I                                                         ______________________________________                                                 FIBER PROPERTIES                                                                    D.S.            TENSILE                                             DESCRIP-  ACETATE/        PROPERTIES                                     EX.  TION      FORMATE    DPF  TEN./ELONG./MOD.                               ______________________________________                                        A    Chitin    1.0/0.0    15.7 1.3 gpd/2.6%/107 gpd                           B    Chitin    2.9/0.0    7.0  2.5 gpd/7.3%/90 gpd                                 Acetate                                                                  1    Chitin    2.0/0.0    4.5  4.3 gpd/4.5%/169 gpd                                Acetate                                                                  2    Chitin    1.4        5.4  5.9 gpd/6.4%/206 gpd                                Acetate                                                                  3    Chitin    2.0/0.3    5.1  5.9 gpd/6.8%/162 gpd                                Acetate/                                                                      Formate                                                                  4    Chitosan  0.4/1.4    19.1 7.0 gpd/6.8%/194 gpd                                Acetate/                                                                      Formate                                                                  5    Chitosan  0.3/1.5    21.4 6.2 gpd/5.8%/185 gpd                                Acetate/                                                                      Formate                                                                  ______________________________________                                         D.S. = degree of substitution, these fiber values can differ from those o     the starting polymer because some partial deesterification may occur          during conversion to fibers                                                   DPF = denier per filament                                                     Ex. = Example or run designation                                         

                                      TABLE II                                    __________________________________________________________________________    SPINNING PARAMETERS                                                           Parameters                                                                             Run A                                                                             Run B                                                                             Ex. 1                                                                             Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex. 5                                        __________________________________________________________________________    % Solids 13.5%                                                                             15% 15% 15% 15% 17% 15%                                          Spinneret                                                                     No. of Holes                                                                           10  1   1   5   1   1   20                                           Dia. of Holes                                                                          0.0102                                                                            0.0076                                                                            0.0076                                                                            0.0076                                                                            0.0076                                                                            0.0127                                                                            0.0076                                       (cm)                                                                          Jet Velocity                                                                           15.2                                                                              29.9                                                                              16.6                                                                              1.5 20.0                                                                              12.0                                                                              3.4                                          (M/min)                                                                       Air Gap (cm)                                                                           1.25                                                                              1.4 1.1 1.3 1.4 1.0 1.9                                          Coagulation Bath                                                                       0   1   8   16  -20 5   -11                                          Temp. (°C.)                                                            Wind-up Rate                                                                           15.5                                                                              24  40  21.3                                                                              17  9.9 6.8                                          (M/min)                                                                       __________________________________________________________________________

What is claimed is:
 1. A process for preparing chitin acetate/formatefiber comprising forming an anisotropic solution of chitinacetate/formate in a solvent of a mixture of trichloroacetic acid andmethylene chloride and spinning the solution through an air gap into acoagulating bath to form a fiber whereby the fiber has an as-spuntenacity of greater than 4 grams per denier.
 2. The process of claim 1wherein the solvent is a 60/40 by weight mixture of trichloroacetic acidand methylene chloride.
 3. The process of claim 2 wherein the percentsolids in the spinning solution is 15%.